Anti-lock braking systems for vehicles including automobiles, aircraft, railways and trucks have been used for a number of years. The need for such systems is especially acute in the trucking field, especially for articulated trucks to prevent loss of control which could cause jackknifing on slippery road surfaces during braking.
Many types of anti-lock braking systems utilize a sensing device which constantly monitors wheel speed and produces signals representative of the wheel speed which are sent to a logic portion of the system. The logic portion calculates rotational speed and acceleration or deceleration of the wheel to determine impending wheel lock and therefore potential skid situations. The system further comprises modulating valves which, when actuated, regulate braking fluid pressure. The logic unit modulates the valves based upon the relative rotational speed of the wheels to maintain maximum braking pressure without inducing wheel lock.
The most popular type of sensing device is a magnetic pickup which is actuated by an exciter ring. The exciter ring is a ring structure with teeth projecting from one face. The exciter ring is mounted on a hub assembly which rotates. The magnetic pickup is mounted adjacent to the exciter ring on a non rotating member such as an axle support or housing. Each time one of the teeth of the exciter ring passes the magnetic pick up, an electrical pulse is generated. The logic portion of the anti-lock braking system can analyze these pulses to determine the acceleration or deceleration rate of the rotating wheel and thereby send any correction signals required to the modulating valves.
The spacing between the exciter ring and the magnetic pick up is extremely critical. Should the gap between the sensor or pick up and the exciter ring vary, due to out of roundness or eccentricity of the exciter ring, the sensor may fail to read the interruptions or teeth of the exciter ring. This will cause the sensor to mistakenly indicate to the logic component of the anti-lock braking system that the associated wheel has locked and a skid is occurring. The logic component of the system may then release braking pressure on that wheel, thereby unnecessarily lowering the braking effectiveness of that wheel.
A common prior art method of attaching the exciter ring to the hub is by a press fit which requires precision machining the hub and precision machining the exciter ring. The hub can be cooled and the exciter ring heated prior to assembly. Referring to FIG. 1 a hub 10 is machined on surface 12. Both the diameter and the depth of the flat is machined. The exciter ring 20 is machined on the inside surface 28 for both diameter and depth and on the face of the teeth 24. The exciter ring 20 was then press fitted in an interference relationship onto hub 10. Although this method was successful, the cost of machining was excessive and the potential existed for the exciter ring to loosen from the hub.
The present invention overcomes the cost of machining and potential loosening by casting the exciter ring integral with the hub.